Process for the manufacture of spinnerets for melt spinning



March 23, 1965 s ms 3,174,364

PROCESS FOR THE MANUFACTURE OF SPINNERETS FOR MELT SPINNING OriginalFiled Sept. 26. 1960 J.G. SIMS BY im, m. ma

ATTORNEY United States Patent 3,174,364 PROCESS FOR THE MANUFACTURE OFSPW- NERETS FOR MELT SPINNING James G. Sims, Pensacola, Fla, assignor toMonsanto Company, a corporation of Delaware Original application Sept.26, 196%, Ser. No. 58,288. Divided and this application Apr. 15, 1963,Ser. No. 272,961

4 Claims. (Cl. 76-107) This invention relates to a process formanufacturing spinnerets adapted for melt spinning highly polymericsubstances. More particularly, the invention relates to a process formaking new and improved spinnerets adapted for melt spinning syntheticthermoplastic polymers into filaments having a central hole extendingaxially thereof.

As is well known in the manufacture of man-made filaments from syntheticpolymers as viscous polymer is forced, such as being pumped, throughsmall holes in a metal spinneret, a die-like plate having a desirednumber of small orifices extending therethrough. In the production ofsynthetic melt-spun filaments molten polymer is forced through theorifices in the spinneret by pressure; and the resulting molten streamsof polymer solidify and harden upon being cooled by an ambient stream ofrelatively cold air or other inert gas. The synthetic filaments, such asnylon-66 as conventionally produced, have the appearance of smooth solidcylindrical rods when viewed under a microscope. Among some of thedisadvantages associated with melt-spun filaments compared to naturallyoccurring fibers such as cotton and wool are their low capacity forabsorbing moisture, lower insulating power, lower covering power, andundesirable slick hand or feeling.

Many methods and devices are known for imparting some of the desirableproperties of natural fibers to meltspun filaments. One approach hasbeen to provide the melt-spun filaments with a continuous central holeor opening along their lengths. However, efforts along this linegenerally have not been successful in producing meltspun filamentspossessing a hollow space extending continuously along their lengths. Inaccordance with a known device suggested for use in the production ofwetspun filaments having a central opening, a solid core is positionedconcentrically within each spinneret orifice during the spinningoperation, the core being suspended by a transverse piece or cross baron the inlet side of the spinneret. In such device the polymericsubstance to be spun upon entering the orifices in the spinneretsurrounds the solid core, the objective being to cause the polymericsubstance to assume an annular path so that a central hollow spaceexists in each of the ultimate filaments. However, such a device cannotbe used successfully in melt spinning, since the extruded streams remainin a molten condition several milliseconds; with low pressure within theinterior, any hollow space tends to collapse upon the exodus of thestreams from the spinneret orifices. The collapsed structure fusestogether interiorly with the result that the filaments so-produced donot possess the desired continuous central opening.

It has been foundthat spinnerets with specially arranged slotted holescan be used advantageously for producing centrally hollow filaments frommolten synthetic thermoplastic fiber-forming polymer. In such anarrangement for each filament produced there is provided an orificialgrouping of a plurality of elongated segments or parts permittingpassage therethrough of molten fiber-forming polymer. The segments aredisposed with respect to each other within each orificial group in sucha manner that the ends of the plurality of molten streams of polymersextruded through the segments within the orificial group- 3,l?4,354Patented Mar. 23, 3965 ing coalesce endwise shortly after issuing fromthe orifices. Fabrication of such orificial grouping in a spinneret isquite expensive and is fraught with difiiculties. Moreover, because ofthe structural weakness of the support, the central partition betweenopposed segments may break out during spinning, resulting in thenecessity of immediate shutdown of the spinning operation; to assurecoalescense of the plurality of streams, the walls of the orifices mustbe very accurately machined and finished. Furthermore, during spinneretcleaning operations orifice edges are easily damaged and are thereafterextremely troublesome or impossible to repair. Thus, such spinnerets.are very difiicult to make even at great expense and the effectiveservice lives of the spinnerets are quite short.

It is a primary object of the invention to provide a new process formanufacturing improved spinnerets with which hollow melt-spun filamentscan be made, said spinnerets overcoming the disadvantages anddiificulties of the known spinnerets.

It is another object of the invention to provide the art with a noveland improved method for making spinnerets with which hollow melt-spunfilaments can be made.

Other objects and advantages of the present invention will becomeapparent from the description of the invention which follows.

In accordance with the present invention, it is now possible with thespinnerets hereindescribed to produce filaments by the melt-spinningprocess, said filaments having a continuous central opening therein.Into a spinneret plate of the type conventionally employed for themelt-spinning operation a hole or a plurality of spaced holes are formedin ,the first step by suitable means such as by drilling, grinding orpunching with a suitable apparatus. A conventional spinneret plate isusually composed of stainless steel of sufficient thickness to withstandthe normal extrusion pressure and mechanical forces involved during meltspinning. It will be appreciated that these forces will vary dependingon'the polymeric material to be melt spun. Next, pieces of metal of thesame or different type from the metal of which the plate is made areshaped in a suitable manner so that only three.

or more portions of the outer periphery thereof will snugly engage theinside periphery of the hole upon in serting such a piece in one of saidholes, thereby leaving a plurality of open spaces extending axiallythrough the spinneret plate and clustered around the inserted metalmembers or pieces to form an orificial grouping. Preferably, theinserted pieces are of such length that the bottom thereof is positionedin the same plane as the bottom of the spinneret plate. The verticalsurfaces of the inserted metal pieces and the inner vertical surfaces ofthe spinnerets except where they engage each other define a plurality ofelongated openings through which molten polymer may be pumped in asuitable manner. The molten polymer is extruded through the openingsgrouped around the metal pieces disposed centrally of the orificialgroupings, the streams of each group are guided so that they coalesceendwise to form a consolidated periphery leaving a hollow central holein the resulting filaments. Preferably the plurality of openings definedby the vertical surfaces of the metal pieces and spinneret plate assumethe form of a discontinuous arcuate segmented configuration but mayassume any arbitrary configuration of unconnected openings provided thatthe extruded polymer streams in an orificial grouping will coalesce toform a filament having a central hole. For example, the openings in theorificial grouping may have the form of a discontinuous polygon.

The novel features which are believed to be characteristic of theinvention are set forth with particularity in the appended claims. Theinvention itself both as to its 3 organization and method of operationcan be best understood by reference to the following description takenin conjunction with the accompanying drawing in which:

FIGURE 1 is a transverse cross-sectional view illustrating on anenlarged scale a hollow filament which may be prepared by the use of aspinneret manufactured in accordance with the present invention;

FIGURE 2 is an elevational view illustrating on an enlarged scale theproduction of one hollow filament produced by the melt-spinningprocedure, employing the spinneret constructed in accordance with theinvention;

FIGURE 3 is a central longitudinal sectional view on an enlarged scaleillustrating a part of a spinneret plate having a metal piece insertedin the bottom portion of the cylindrical orifice therein;

FIGURE 4 is a perspective view of one type of metal insert readied forinsertion in a hole formed in the spinneret plate;

FIGURE 5 is a bottom view of part of a spinneret plate illustrating themetal insert shown in FIGURE 4 placed in a circular orifice extendingthrough the said plate;

FIGURE 6 is a perspective view of a metal insert having four radiallyextending legs whose extremities are adapted for firm assemblage in acircular orifice;

FIGURE 7 is a bottom view of part of a spinneret plate illustrating themetal insert shown in FIGURE 6 placed in a circular orifice extendingthrough the said plate;

FIGURE 8 is a perspective view of a metal insert having four extendinglegs, two of which are parallel and extend in opposite directions andthe remaining two of which are similarly arranged but extend at rightangles with respect to the other legs, the extremities of said legsbeing adapted for snug engagement in a hole of square cross section inthe spinneret plate; and

FIGURE 9 is a bottom view of part of a spinneret plate illustrating themetal insert shown in FIGURE 8 placed in the hole extending through thesaid plate.

Referring to FIGURE 1, there is shown in cross section an axially hollowfilament which may be produced by employing a spinneret manufactured inaccordance with the present invention. Numeral 1 indicates theconsolidated filament obtained by the coalescing of the outer verticalends of a plurality of extruded elongated streams of molten polymer.Extending continuously through the length of the filament is an axialhole 2.

In FIGURE 2 the formation of the filament is shown with moreparticularity. Part of a spinneret plate 3 can be seen in this figure. Ahole 4 consists of two portions of different diameters. The top portion5 has a diameter larger than that of the bottom portion 6. Inserted inthe bottom portion in firm force-fitted relation is a metal insert 7which engages the inside periphery of portion 6 at a plurality of spacedpoints. Molten polymer from a suitable source is forced downwardlythrough the top portion 5 in operation and then through the segmentedannuli provided by the elongated open spaces between the insideperiphery of hole portion 6 and the opposed spaced apart outsideperiphery of insert 7. Where the extremities of insert 7 engage theinside periphery of the hole portion 6, the molten polymer flowingthrough the hole portion 5 is subdivided into a plurality of streams.

During melt spinning of filaments at the relatively high spinning speedsand the concomitant extrusion pressure, as is required economically incommercial practice today, the streams of polymer at the instant theyleave the openings in the spinneret plate tend to expand to form abulbous protrusion 8. Because of the subdividing of the stream, slits 9exist between the streams and extend for a short distance below thespinneret converging at point 10 where the molten streams of polymercoalesce to form one coherent stream which solidifies during its travelthrough a cooling medium to form a filament 1 having a consolidatedperiphery and an axially extending hole 2. It will be perceived that thepassage of air through the slits 9 equalizes inside and outside airpressure.

In FIGURE 3 a spinneret made in accordance with the present invention isshown in cross section taken centrally of hole 4; the insert 7 isarranged in tight force-fitted relation in the hole portion 6. Since theparts of the outside periphery of insert 7 are spaced from the insideperiphery of portion 6, a plurality of passageways 11 forming oneorificial grouping are provided through which molten polymer moves inoperation. It will be appreciated that the number of orificial groupingsdisposed in one spinneret plate will be determined by the size of theplate and the number of hollow filaments desired in one bundle. As theextruded streams in each group move downwardly from the bottom of thespinneret, they are caused to be consolidated into unitary hollowfilaments.

The insert 12 as shown in FIGURE 4 has a triangular cross sectionapproximating that of an equi-angular triangle having slightly angularapexes. These apexes of insert 12 are rounded to correspond with theinside curvature of the hole in the spinneret in which it is to beinserted. Insert 12 is shaped by conventional machining procedures ormolded by conventional methods. For convenience, an elongated rod or barof suitable size and material can be shaped, such as by wire-drawing orby using a shaper, into the three-sided shape and the resulting rod orbar cut into pieces of appropriate lengths adapted for insertion in ahole in a spinneret plate.

In FIGURE 5 insert 12 is mated securely in hole 4 of spinneret plate 3so as to provide for the emission of three streams of polymer from thesegmented annuli 13. In such arrangement three passageways forming oneorificial grouping are provided through which molten polymer moves inoperation. The three streams issuing from each orificial group arebrought together just below the bottom of the spinneret to produce anintegral filamentary structure having a central, longitudinallyextending hole.

The insert 14 as shown in FIGURE 6 has a main body section 15 ofcircular cross section with four circumferentially disposed, equi-spacedextending legs 16 ter'- minating with convexly rounded extremities. Theradius of curvature of the arcuate extremities is substantiallyidentical to the radius of the orifice in the spinneret into which it isplaced. As above in connection with the method of producing insert 12,insert 14 can be shaped or molded by known procedures to form anelongated rod or the like, the shaped rod being cut into desiredlengths.

In FIGURE 7 insert 14 is mated securely in a hole in spinneret plate 3so as to provide for the emission of four streams of polymer fromsegmented annuli 17, 18, 19 and 20. In such arrangement four polymerpassageways forming one orificial grouping are provided through whichmolten polymer moves during melt spinning. To produce a hollow filamentthe four streams issuing from each orificial group are brought togetherjust below the bottom of the spinneret to fuse into an integralfilamentary struc ture having a central longitudinally extending hole.

The insert 21 as shown in FIGURE 8 has a main body section 22 of squarecross section with four extending legs 23 adapted to fit snugly in asquare hole and to" withstand extrusion pressures. As above inconnection with the method of producing insert 12, insert 21 can beshaped or molded by known procedures to form an elongated rod or thelike, the shaped rod being cut into pieces of desired lengths.

In FIGURE 9 insert 21 is mated securely in a hole in spinneret plate 3so as to provide for the emission of four streams from polygonallyarranged slots 24, 25, 26 and 27.

The actual dimensions of the openings comprising an orificial groupdepend upon the characteristics of the polymer, the filament size 01'denier, the spinning speed, and other factors in the particularmelt-spinning process. in the production of filaments for textile andindustrial yarns the circumference of the open hole in the spinneretplate (without insert) is preferably within the range of 0.040 inch to0.80 inch. To insure proper coalescence.-

of the individual polymer streams, relative proportions betweendimensions must be maintained within certain limits. The total area ofthe segments or annuli in an orificial grouping shall be between 30percent and 60 percent of the area defined by the open hole. The ratioof the maximum length of each segment to its maximum width should not beless than 3; for example, in FIGURE 9 rectangular slots 24, 25, 26 and27 ought to have a length to width ratio not less than 3; similarly, inFIG- URE 5, the ratio of the length of the chord to the height of thesegment on the chord must not be less than 3. Furthermore, the minimumdistance separating the orificial segments must not exceed the maximumwidth and is preferably not greater than one-half the maximum width.

The spinneret of the present invention can be used to produce filamentsfrom any suitable substance that can be melt spun. Specific polymericmaterials capable of being melt spun include: nylon-66, nylon-6,nylon-4, nylon-610, nylon-ll, and their filament-forming copolymersthereof, e.g., nylon-6/ 66, 6/610/ 66, etc.; polyesters derived fromterephthalic acid and ethylene glycol and from terephthalic acid andbis-l,4-(hydroxymethyl)- cyclohexane; polyethylene and polypropylene,and other substances.

It is apparent from the foregoing description that this inventionrepresents a material advance in the art of manufacturing spinnerets forproducing hollow filaments. Heretofore the processes have been slow andcostly and the spinnerets had a limited service life. Existingspinnerets for producing solid filaments can be converted with rathernominal expense to spinnerets from which hollow filaments can beproduced. For example, an insert of the type above-described can beplaced in reamed orifices formed in a spinneret normally used in meltspinning. The savings in time, capital investment in equipment,maintenance costs and melt-spinning efficiency compared with knownspinnerets and methods of producing same for use in the formation ofhollow filaments show the present invention to be distinctlyadvantageous.

It is apparent that many widely different embodiments of this inventioncan be made without departing from the spirit and scope thereof; and,therefore, it is not intended to be limited except as indicated in theappended claims.

This application is a divisional application of copending applicationSerial No. 58,288, filed September 26, 1960, now abandoned.

What is claimed is:

1. A process for the manufacture of a spinneret adapted for meltspinning thermoplastic polymers into filaments having a continuousaxially extending hole comprising forming an extrusion hole extendingthrough a plate, shaping an insert member so that said member isengageable with the inside periphery of said extrusion hole along atleast three portions of its periphery only to provide a plurality oflaterally elongated open spaces extending through the said plate, thetotal lateral cross-sectional area of the open spaces in the orificialgrouping being between 30 percent and 60 percent of the lateralcross-sectional area of the said extrusion hole, and forcefitting saidinsert member so-shaped into said extrusion hole in tightly assembledrelation therewith so that the bottom of said insert member is flushwith the bottom of the plate.

2. A process for the manufacture of a spinneret adapted for meltspinning thermoplastic polymers into filaments having a continuousaxially extending hole comprising forming a plurality of extrusion holesextending through a plate, shaping an insert member for each extrusionhole so that said member is engageable with the inside periphery of itsrespective extrusion hole along at least three portions of its peripheryonly to provide a plurality of laterally elongated open spaces extendingthrough the said plate, the total lateral cross-sectional area of theopen spaces in each orificial grouping being between 30 percent and 60percent of the lateral cross-sectional area of the correspondingextrusion hole, and force-fitting said insert member so-shaped into itsrespective extrusion hole in tightly assembled relation therewith sothat the bottom of said insert member is flush with the bottom of theplate.

3. A process for the manufacture of a spinneret adapted for meltspinning thermoplastic polymers into filaments having a continuousaxially extending hole comprising forming an extrusion orifice extendingthrough a metal plate and having a cylindrical shape of two poritons ofdifferent diameter, shaping a metal insert member of triangular crosssection having rounded apexes corresponding to the curvature of theinside periphery of the extrusion orifice, said insert member beingengageable with the inside periphery of said extrusion orifice at threeportions of the periphery only to provide three elongated segmentedannuli extending through the said plate, the total lateralcross-sectional area of the annuli in the orificial grouping beingbetween 30 percent and 60 percent of the lateral cross-sectional area ofthe extrusion orifice, the lengthzwidth ratio of the annuli not beingless than 3, and the distance separating the adjacent ends of the annulinot exceeding the width of the annuli, and force-fitting said insertmember so-shaped into the portion of the extrusion orifice of smallerdiameter in tightly assembled relation therewith so that the bottom ofsaid insert member is flush with the bottom of the plate.

4. A process for the manufacture of a spinneret adapted for meltspinning thermoplastic polymers into filaments having a continuousaxially extending hole comprising forming an extrusion orifice extendingthrough a metal plate and having a cylindrical shape of two portions ofdifferent diameters, shaping a metal insert member having a main body ofcircular cross section with four legs extending radially therefrom, theextremities of said legs being rounded to correspond to the curvature ofthe inside periphery of the said extrusion orifice, said insert memberbeing engageable with the inside periphery at said extrusion orifice atthe extremities of said legs only to provide four elongated segmentedannuli extending through the said plate, the total lateralcross-sectional area of the annuli in the orificial grouping beingbetween 30 percent and 60 percent of the lateral cross-sectional area ofthe extrusion orifice, the lengthzwidth ratio of the annuli not beingless than 3, and the distance separating the adjacent ends of the annulinot exceeding the width of the annuli, and force-fitting said insertmember so-shaped into the portion of the extrusion orifice of smallerdiameter in tightly assembled relation therewith so that the bottom ofsaid insert member is flush with the bottom of the plate.

References Cited by the Examiner UNITED STATES PATENTS 1,597,928 8/26Simons 76-107 2,820,374 1/58 De Wolf 76---107 2,952,071 9/60 Burt 29-525XR 2,962,810 12/60 Gilmore 29-525 XR 3,102,439 9/ 63 Martin et al.76-107 FOREIGN PATENTS 22,568 1913 Great Britain. 843,179 8/60 GreatBritain.

WHITMORE A. WILTZ, Primary Examiner.

1. A PROCESS FOR THE MANUFACTURE OF A SPINNERET ADAPTED FOR MELTSPINNING THERMOPLASTIC POLYMERS INTO FILAMENTS HAVING A CONTINUOUSAXIALLY EXTENDING HOLE COMPRISING FORMING AN EXTRUSION HOLE EXTENDINGTHROUGH A PLATE, SHAPING AN INSERT MEMBER SO THAT SAID MEMBER ISENGAGEABLE WITH THE INSIDE PERIPHERY OF SAID EXTRUSION HOLE ALONG ATLEAST THREE PORTIONS OF ITS PERIPHERY ONLY TO PROVIDE A PLURALITY OFLATERALLY ELONGATED OPEN SPACES EXTENDING THROUGH THE SAID PLATE, THETOTAL LATERAL CROSS-SECTIONAL AREA OF THE OPEN SPACES IN THE ORIFICALGROUPING BEING BETWEEN 30 PERCENT AND 60 PERCENT OF THE LATERALCROSS-SECTIONAL AREA OF THE SAID EXTRUSION HOLE, AND FORCEFITTING SAIDINSERT MEMBER SO-SHAPED INTO SAID EXTRUSION HOLE IN TIGHTLY ASSEMBLEDRELATION THEREWITH SO THAT THE BOTTOM OF SAID INSERT MEMBER IS FLUSHWITH THE BOTTOM OF THE PLATE.